1. Field of the Invention
The present invention relates to a brake traction control system, and more particularly, to a braking pressure threshold limiting method of a brake traction control system for climbing a slope, in which, in order to prevent degradation of a climbing performance of a vehicle at the time of performing a Traction Control System (“TCS”) control when the vehicle is accelerated on a split road surface of the slope (a road surface on which the frictions of left and right wheels of the vehicle are different from each other), a maximum value of a braking pressure is limited to a braking pressure applied when a high-frictional driving wheel suffers from instability so that the climbing performance on the split road surface can be improved. Here, the instability refers to a phenomenon that when a low-frictional driving wheel of a vehicle slips, and a braking pressure applied to the low-frictional driving wheel is excessive, a high-frictional driving wheel, which is positioned opposite to a low-frictional driving wheel and connected to the low-frictional driving wheel via a differential gear, slips.
2. Description of the Prior Art
A vehicle brake refers to an apparatus that functions to reduce a speed of a running vehicle or to stop the vehicle.
The brake uses a hydraulic force, which is applied depending on a driver's brake pedal operating force. Through a simple method of locking a rotating vehicle wheel not to rotate, such a brake may not implement an optimum braking performance according to a travel condition of the vehicle and a condition of a road surface. In order to overcome such a limit of the brake system, an Anti-Lock Brake System (“ABS”) configured to properly control a braking pressure applied to a wheel depending on a slip rate calculated based on a wheel speed so as to prevent the wheel from being locked, or a Traction Control System (“TCS”) configured to control a driving force of an engine so as to prevent an excessive slip at a time of sudden unintended acceleration or sudden acceleration is used to improve the stability of the vehicle. Here, such a TCS is disclosed in Korean Patent Laid-Open Publication No. 2003-0093457.
Further, a Brake Traction Control System (“BTCS”) has been proposed in which the BTCS performs a control to prevent a slip phenomenon between wheels and a road surface when the vehicle starts so that the vehicle can smoothly start.
The BTCS control is performed when the vehicle is accelerated on a split road surface in which the frictional forces of left and right road surfaces are different from each other (a road surface on which a difference in frictional coefficient is large between the wheels of the both side of the vehicle). At this time, when the braking pressure applied to a slipping wheel is excessive, the torque of a low-frictional (low-u) driving wheel is transmitted to an opposite side high-frictional (high-u) driving wheel connected thereto via a differential apparatus, thereby causing the high-frictional driving wheel to spin. Thus, the yaw motion of the vehicle suddenly deteriorates such that a vehicle behavior desired by the driver cannot be achieved. At this time, the instability of the high-frictional driving wheel is rapidly sensed to perform a control so as to reduce the excessive braking pressure of the spinning low-frictional driving wheel.
However, when the braking pressure applied to the slipping low-frictional driving force is excessive while climbing an uphill road, on which a split road surface is formed, such as a slope, the high-frictional driving wheel becomes unstable. At this time, a controller of the BTCS applies a consistent pressure depending on a spin amount so as to adjust the spin occurring in the low-frictional driving wheel to a target spin amount. Thus, the continuous unstable state of the high-frictional driving wheel consistently occurs and makes the climbing of the vehicle difficult.